//
// Created by user on 2022/2/24.
//
#include <vector>
#include <unordered_map>
using namespace std;
int singleNumber(vector<int>& nums) {
    unordered_map<int, int> map;
    for (int num:nums)map[num]++;

    for(auto &x:map){
        if(x.second==1){return x.first;}
    }
    return -1;
}